1. Field of the Invention
The present invention relates to a p-type ZnO semiconductor film and a process for preparation thereof.
2. Description of Related Art
In order to realize the new generation of electronic devices, e.g., transparent electronic circuits and ultraviolet light-emitting diodes, using oxide semiconductors, it is essential to develop p-type oxide semiconductors. Zinc oxide (ZnO), because of its high potential, has been recently noted as a promising material for such p-type oxide semiconductors and the associated research and development have been actively conducted.
However, it is extremely difficult to prepare p-type ZnO and only a very few successful examples are reported. As a representative of such successful examples, a codoping method is known which involves simultaneous doping of an acceptor impurity and a donor impurity (see, for example, Japanese Patent Laying-open No. 2001-48698 and PCT Int. Publication No. WO 00/22202).
It is however reported that the follow-up attempts of the reported codoping method by researchers resulted in the failure to obtain the p-type ZnO (K. Nakahara et al., Journal of Crystal Growth, 237-239 (2002), pp. 503-508; M. Sumiya et al., Applied Surface Science, 223 (2004), pp. 206-209; and others). As such, a highly reproducible process to obtain the p-type ZnO has not been established to date.